[whatwg] need a way to set output format from StreamRecorder

Ian Hickson ian at hixie.ch
Mon Feb 14 14:39:49 PST 2011

On Fri, 19 Nov 2010, Per-Erik Brodin wrote:
> We are about to start implementing stream.record() and StreamRecorder. 
> The spec currently says that “the file must be in a format supported by 
> the user agent for use in audio and video elements” which is a 
> reasonable restriction. However, there is currently no way to set the 
> output format of the resulting File that you get from recorder.stop(). 
> It is unlikely that specifying a default format would be sufficient if 
> you in addition to container formats and codecs consider resolution, 
> color depth, frame rate etc. for video and sample size and rate, number 
> of channels etc. for audio.
> Perhaps an argument should be added to record() that specifies the 
> output format from StreamRecorder as a MIME type with parameters? Since 
> record() should probably throw when an unsupported type is supplied, it 
> would perhaps be useful to have a canRecordType() or similar to be able 
> to test for supported formats.

I haven't added anything here yet, mostly because I've no idea what to 
add. The ideal situation here is that we have one codec that everyone can 
read and write and so don't need anything, but that may be hopelessly 
optimistic. In the meantime I encourage implementors to experiment with 
this (with all the APIs vendor-prefixed of course) to work out what the 
API should look like. Implementation experience is the main thing that 
will drive this forward, I think.

Ian Hickson               U+1047E                )\._.,--....,'``.    fL
http://ln.hixie.ch/       U+263A                /,   _.. \   _\  ;`._ ,.
Things that are impossible just take longer.   `._.-(,_..'--(,_..'`-.;.'

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